Cannula with associated filter and methods of use during cardiac surgery

ABSTRACT

Devices and methods for filtering blood. The devices generally comprise: a mesh for filtering blood flowing within a blood vessel, particularly within an artery such as the aorta; a structure adapted to open and close the mesh within the blood vessel; and a means to actuate the structure. The methods generally include the following steps: introducing a mesh into a blood vessel to entrap embolic material; adjusting the mesh, if necessary, during the course of filtration; and removing the mesh and the entrapped foreign matter from the blood vessel. Additionally, visualization techniques are used to ensure effective filtration.

This is a continuation of U.S. application Ser. No. 08/842,727, filedApr. 16, 1997, now U.S. Pat. No. 5,989,281, which is acontinuation-in-part of U.S. application Ser. No. 08/640,015, filed Apr.30, 1996, now U.S. Pat. No. 5,769,816, which is a continuation-in-partof U.S. application Ser. No. 08/584,759, filed Jan. 11, 1996, nowabandoned, which is a continuation-in-part of U.S. application Ser. No.08/580,223, filed Dec. 28, 1995, now abandoned, which is acontinuation-in-part of U.S. application Ser. No. 08/553,137, filed Nov.7, 1995, now abandoned. Each of the above-identified applications andpatents are expressly incorporated herein by reference in theirentirety.

FIELD OF THE INVENTION

The present invention relates generally to blood filter devices fortemporary placement in a blood vessel to capture embolic material, andmore particularly to a cannula device having an associated blood filterfor placement in a blood vessel to carry blood to an artery from abypass-oxygenator system and to entrap embolic material in the vessel.More particularly, the invention relates to a blood filter device to beplaced in the aorta during cardiac surgery. The present invention alsorelates to methods for temporarily filtering blood to entrap and removeembolic material and, more particularly, to methods for protecting apatient from embolization which has been caused by procedures such asincising, clamping, and clamp release which can dislodge atheromatousmaterial from the artery.

BACKGROUND OF THE INVENTION

There are a number of known devices designed to filter blood. The vastmajority of these devices are designed for permanent placement in veins,in order to trap emboli destined for the lungs. For example, Kimmell,Jr., U.S. Pat. No. 3,952,747 (this and all other references cited hereinare expressly incorporated by reference as if fully set forth in theirentirety herein), discloses the so-called Kimray-Greenfield filter. Thisis a permanent filter typically placed in the vena cava comprising aplurality of convergent legs in a generally conical array, which arejoined at their convergent ends to an apical hub. Each leg has a benthook at its end to impale the internal walls of the vena cava.

Cottenceau et al., U.S. Pat. No. 5,375,612, discloses a blood filterintended for implantation in a blood vessel, typically in the vena cava.This device comprises a zigzagged thread wound on itself and a centralstrainer section to retain blood clots. This strainer section comprisesa meshed net and may be made from a biologically absorbable material.This device is also provided with attachment means which penetrate intothe wall of the vessel.

Gunther et al., U.S. Pat. No. 5,329,942, discloses a method forfiltering blood in the venous system wherein a filter is positionedwithin a blood vessel beyond the distal end of a catheter by apositioning means guided through the catheter. The positioning means islocked to the catheter, and the catheter is anchored to the patient. Thefilter takes the form of a basket and is comprised of a plurality ofthin resilient wires. This filter can be repositioned within the vesselto avoid endothelialization within the vessel wall.

Similarly, Lefebvre, French Patent No. 2,567,405, discloses a bloodfilter for implantation by an endovenous route into the vena cava. Thefilter is present in the form of a cone, and the filtering means mayconsist of a flexible metallic grid, or a flexible synthetic or plasticgrid, or a weave of synthetic filaments, or a non-degradable or possiblybio-degradable textile cloth. In order to hold the filter within thevein, this device includes flexible rods which are sharpened so thatthey may easily penetrate into the inner wall of the vena cava.

There are various problems associated with permanent filters. Forexample, when a filter remains in contact with the inner wall of thevena cava for a substantial period of time, endothelialization takesplace and the filter will subsequently become attached to the vena cava.This endothelialization may cause further occlusion of the vessel,thereby contributing to the problem the filter was intended to solve.Except for the Gunther device, these prior art filters do not addressthis problem.

A temporary venous filter device is disclosed in Bajaj, U.S. Pat. No.5,053,008. This device treats emboli in the pulmonary artery which,despite its name, is in fact a vein. The Bajaj device is an intracardiaccatheter for temporary placement in the pulmonary trunk of a patientpredisposed to pulmonary embolism because of hip surgery, stroke orcerebral hemorrhage, major trauma, major abdominal or pelvic surgery,neurosurgery, neoplasm, sepsis, cardiorespiratory failure orimmobilization.

The Bajaj device includes an umbrella made from meshwork which trapsvenous emboli before they reach the lungs. This device can also lyseemboli with a thrombolytic agent such as tissue plasminogen activator(TPA), destroy emboli with high velocity ultrasound energy, and removeemboli by vacuum suction through the lumen of the catheter. This verycomplex device is designed for venous filtration and is difficult tojustify when good alternative treatments exist.

There are very few intravascular devices designed for arterial use. Afilter that functions not only in veins, but also in arteries mustaddress additional concerns because of the hemodynamic differencesbetween arteries and veins. Arteries are much more flexible and elasticthan veins and, in the arteries, blood flow is pulsatile with largepressure variations between systolic and diastolic flow. These pressurevariations cause the artery walls to expand and contract. Blood flowrates in the arteries vary from about 1 to about 5 L/min.

Ginsburg, U.S. Pat. No. 4,873,978, discloses an arterial device. Thisdevice includes a catheter that has a strainer device at its distal end.This device is normally used in conjunction with non-surgicalangioplastic treatment. This device is inserted into the vesseldownstream from the treatment site and, after the treatment, thestrainer is collapsed around the entrapped emboli, and the strainer andemboli are removed from the body. The Ginsburg device could notwithstand flow rates of 5 L/min. It is designed for only small arteriesand therefore could not capture emboli destined for all parts of thebody. For example, it would not catch emboli going to the brain.

Ing. Walter Hengst GmbH & Co, German Patent DE 34 17 738, disclosesanother filter which may be used in the arteries of persons with a riskof embolism. This filter has an inherent tension which converts thefilter from the collapsed to the unfolded state, or it can be unfoldedby means of a folding linkage system. This folding linkage systemcomprises a plurality of folding arms spaced in parallel rows along thelongitudinal axis of the conical filter (roughly similar to branches ona tree). The folding arms may be provided with small barbs at theirprojecting ends intended to penetrate the wall of the blood vessel toimprove the hold of the filter within the vessel.

Moreover, da Silva, Brazil Patent Application No. PI9301980A, discussesan arterial filter for use during certain heart operations where theleft chamber of the heart is opened. The filter in this case is used tocollect certain particles not removed on cleaning the surgical site.

What is needed is a simple, safe blood filter for temporary use. Forexample, a temporary arterial device for use during surgery that neithercomplicates nor lengthens the surgical procedure would be desirable.Existing prior art devices are inadequate for this purpose.

SUMMARY OF THE INVENTION

The present invention relates to blood filter devices and methods offiltering blood. The devices of the present invention are adapted tofilter embolic material from the blood. Embolic material or foreignmatter is any particulate matter which may cause complications in thebody if allowed to travel freely in the bloodstream. This particulatematter includes but is not limited to atheromatous fragments ormaterial, and fat.

In one embodiment, the device includes four major elements: a mesh,which filters blood flowing in a blood vessel; an insertion tube adaptedfor placing the mesh into and removing it from the blood vessel; anumbrella frame adapted for connecting the mesh to the insertion tube andfor positioning and maintaining the mesh in a position wherein bloodpasses therethrough; and a means for opening and closing the umbrellaframe.

In another embodiment, the device includes three major elements: a mesh,which filters blood flowing in a blood vessel; an umbrella frame adaptedfor positioning and maintaining the mesh in a position wherein bloodpasses therethrough; and a means for opening and closing the umbrellaframe. The umbrella frame is affixed to a cannula which is inserted intothe blood vessel. In alternative embodiments, the mesh additionally maybe provided to cover the end of the cannula if necessary. Thisadditional mesh simply may be an extension of the mesh of the secondpreferred embodiment, or it may be a separate mesh located either at theend of the cannula or within the cannula.

In another embodiment, the device includes four major elements: acontinuous mesh for filtering blood flowing within a blood vessel; aninflatable donut-shaped balloon adapted to open and close the mesh; aplurality of tie lines to hold the mesh and balloon in place within thebloodstream; and an actuation assembly. In a preferred embodiment, themesh is cone-shaped and four tie lines attached to the inflatableballoon are employed to hold the balloon and the mesh in place forfiltering.

In still another embodiment, the device may include an arterial cannuladisposed within a pressurizing cannula. The pressurizing cannula has aproximal region, a distal region, and an intermediate regiontherebetween, which intermediate region includes a first lumen passingfrom the proximal to distal end and shaped to receive a cannula forblood supply. The distal region may include an associated filtercomprising a mesh which may have a substantially conical shape in anexpanded condition and which may be contracted to a smaller,substantially cylindrical shape. The proximal end of the mesh may beattached to an inflatable, donut-shaped balloon or inflation sealadapted to open and close the mesh. The inflation seal-mesh assembly maybe attached at its proximal end to the pressurizing cannula and, at itsdistal end, may optionally include any of an unbroken continuous mesh, amesh attached to a distal region of the cannula for blood supply, and amesh attached to a distal region of the pressurizing cannula. Thepressurizing cannula will generally include means for inflating anddeflating the inflation seal.

In another embodiment, the device includes a mesh, an arterial cannula,a blood flow diffuser and a structure adapted to open and close the meshwithin the blood vessel, such as an umbrella frame or inflatableballoon. The blood flow diffuser may be located inside or outside of thearterial cannula. In both the intra-cannula and extra-cannula diffuserembodiments, the flow diffuser can be located either proximal or distalto the mesh.

In another embodiment, the device includes a sleeve which, whenunrolled, captures the mesh and the expansion frame adapted to open andclose the mesh. In one embodiment the sleeve may be actuated by controllines which control the unrolling and rolling-up of the sleeve. Thecaptured structure may be an umbrella frame adapted for positioning andmaintaining the mesh in a position wherein blood passes therethrough.Alternatively, the captured structure is an inflatable balloon.

In still another embodiment, the device includes a cannula made in partof a deformable (e.g.) elastomeric material such that the deformablepart of the cannula collapses to absorb the mesh and the correspondingadapted structure upon mesh closure, thereby reducing the profile of theinstrument for vessel introduction.

The methods of the present invention relate to filtering blood flowingwithin a blood vessel, particularly to entrap embolic material, therebyprotecting a patient from embolization. In accordance with one aspect ofthe method of the invention, a patient is protected from embolizationduring surgery while performing a procedure affecting a region of anartery of the patient wherein the artery includes foreign matter on aninside surface thereof at least a portion of which is dislodged as aresult of mechanical or other forces applied during the procedure, bydeploying a removable filtration device in a blood vessel downstream ofone affected region of the artery to entrap the dislodged foreignmatter.

In other embodiments, the methods of the present invention generallyinclude the following steps: introducing a mesh into a blood vessel toentrap embolic material or foreign matter in the blood, positioning themesh, if necessary, and removing the mesh and the entrapped foreignmatter from the blood vessel. Additionally, visualization techniquesincluding transcranial doppler ultrasonography, transesophagealechocardiography, epicardiac echocardiography, and transcutaneous orintravascular ultrasonography in conjunction with the procedure may beused to ensure effective filtration.

In a preferred method, blood is filtered during cardiac surgery, inparticular during cardiac bypass surgery, to protect a patient fromembolization. In this method, the mesh is positioned in the aorta whereit filters blood before it reaches the carotid arteries, brachiocephalictrunk, and left subclavian artery.

The present invention was developed, in part, in view of a recognitionof the occurrence of embolization during cardiac surgery. Emboli arefrequently detected in cardiac surgery patients and have been found toaccount for neurologic, cardiac and other systemic complications.Specifically, embolization appears to contribute significantly toproblems such as strokes, lengthy hospital stays and, in some cases,death. Of the patients undergoing cardiac surgery, 5-10% experiencestrokes and 30% become cognitively impaired. In addition, it has beenrecognized that embolization is often the result of procedures performedon blood vessels such as incising, clamping, and cannulation, whereinmechanical or other force is applied to the vessel. See, for example,Barbut et al., "Cerebral Emboli Detected During Bypass Surgery AreAssociated With Clamp Removal," Stroke, 25(12):2398-2402 (1994), whichis incorporated herein by reference in its entirety. These proceduresare commonly performed in many different types of surgery includingcardiac surgery, coronary artery surgery including coronary arterybypass graft surgery, aneurysm repair surgery, angioplasty, atherectomy,and endarterectomy, including carotid endarterectomy. It has also beenrecognized that reintroducing blood into blood vessels with a cannuladuring these procedures can dislodge plaque and other emboli-creatingmaterials as a result of blood impinging upon the vessel wall at highvelocities. See, for example, Cosgrove et. al., Low Velocity AorticCannula, U.S. Pat. No. 5,354,288. Finally, it has been found that theoccurrence of embolization is more likely in certain types of patients.For example, embolization occurs more frequently in elderly patients andin those patients who have atheromatosis. In fact, atheromatousembolization, which is related to severity of aortic atheromatosis, isthe single most important contributing factor to perioperativeneurologic morbidity in patients undergoing cardiac surgery.

Embolic material, which has been detected at 2.88 mm in diameter, willgenerally range from 0.02 mm (20 μm) to 5 mm, and consists predominantlyof atheromatous fragments dislodged from the aortic wall and air bubblesintroduced during dissection, but also includes platelet aggregateswhich form during cardiac surgery. See Barbut et al., "Determination ofEmbolic Size and Volume of Embolization During Coronary Artery BypassSurgery Using Transesophageal Echocardiography," J. CardiothoracicAnesthesia (1996). These emboli enter either the cerebral circulation orsystemic arterial system. Those entering the cerebral circulationobstruct small arteries and lead to macroscopic or microscopic cerebralinfarction, with ensuing neurocognitive dysfunction. Systemic embolisimilarly cause infarction, leading to cardiac, renal, mesenteric, andother ischemic complications. See Barbut et al., "Aortic AtheromatosisAnd Risks of Cerebral Embolization," Journal of Cardiothoracic andVascular Anesthesia 10(1):24-30 (1996), which is incorporated herein byreference in its entirety.

Emboli entering the cerebral circulation during coronary artery bypasssurgery have been detected with transcranial Doppler ultrasonography(TCD). TCD is a standard visualization technique used for monitoringemboli in the cerebral circulation. To detect emboli using TCD, themiddle cerebral artery of a bypass patient is continuously monitoredfrom aortic cannulation to bypass discontinuation using a 2 MHZpulsed-wave TCD probe (Medasonics-CDS) placed on the patient's temple ata depth of 4.5 to 6.0 cm. The number of emboli is determined by countingthe number of embolic signals, which are high-amplitude, unidirectional,transient signals, lasting less than 0.1 second in duration andassociated with a characteristic chirping sound.

TCD is useful in analyzing the relationship between embolization andprocedures performed on blood vessels. For example, the timing ofembolic signals detected by TCD have been recorded along with the timingof procedures performed during open or closed cardiac surgicalprocedures. One of these procedures is cross-clamping of the aorta totemporarily block the flow of blood back into the heart. It has beenfound that flurries of emboli are frequently detected after aorticclamping and clamp release. During the placement and removal for theclamps, atheromatous material along the aortic wall apparently becomesdetached and finds its way to the brain and other parts of the body.Similarly, flurries of emboli are also detected during aorticcannulation and inception and termination of bypass.

Transesophageal echocardiography (TEE), another standard visualizationtechnique known in the art, is significant in the detection ofconditions which may predispose a patient to embolization. TEE is aninvasive technique, which has been used, with either biplanar andmultiplanar probes, to visualize segments of the aorta, to ascertain thepresence of atheroma. This technique permits physicians to visualize theaortic wall in great detail and to quantify atheromatous aortic plaqueaccording to thickness, degree of intraluminal protrusion and presenceor absence of mobile components, as well as visualize emboli within thevascular lumen. See, for example, Barbut et al., "Comparison ofTranscranial Doppler and Transesophageal Echocardiography to MonitorEmboli During Coronary Bypass Surgery," Stroke 27(1):87-90 (1996) andYao, Barbut et al., "Detection of Aortic Emboli By TransesophagealEchocardiography During Coronary Artery Bypass Surgery," Journal ofCardiothoracic Anesthesia 10(3):314-317 (May 1996), and Anesthesiology83(3A):A126 (1995), which are incorporated herein by reference in theirentirety. Through TEE, one may also determine which segments of a vesselwall contain the most plaque. For example, in patients with aorticatheromatous disease, mobile plaque has been found to be the leastcommon in the ascending aorta, much more common in the distal arch andmost frequent in the descending segment. Furthermore, TEE-detectedaortic plaque is unequivocally associated with stroke. Plaque of allthickness is associated with stroke but the association is strongest forplaques over 4 mm in thickness. See Amarenco et al., "Atheroscleroticdisease of the aortic arch and the risk of ischemic stroke," New EnglandJournal of Medicine, 331:1474-1479 (1994).

Another visualization technique, intravascular ultrasound, is alsouseful in evaluating the condition of a patient's blood vessel. Unlikethe other techniques mentioned, intravascular ultrasound visualizes theblood vessel from its inside. Thus, for example, it is useful forvisualizing the ascending aorta overcoming deficiencies of the othertechniques. In one aspect of the invention, it is contemplated thatintravascular ultrasound is useful in conjunction with devices disclosedherein. In this way, the device and visualizing means may be introducedinto the vessel by means of a single catheter.

Through visualization techniques such as TEE epicardial aorticultrasonography and intravascular ultrasound, it is possible to identifythe patients with plaque and to determine appropriate regions of apatient's vessel on which to perform certain procedures. For example,during cardiac surgery, in particular, coronary artery bypass surgery,positioning a probe to view the aortic arch allows monitoring of allsources of emboli in this procedure, including air introduced duringaortic cannulation, air in the bypass equipment, platelet emboli formedby turbulence in the system and atheromatous emboli from the aorticwall. Visualization techniques may be used in conjunction with a bloodfilter device to filter blood effectively. For example, through use of avisualization technique, a user may adjust the position of a bloodfilter device, and the degree of actuation of that device as well asassessing the efficacy of the device by determining whether foreignmatter has bypassed the device.

It is an object of the present invention to eliminate or reduce theproblems that have been recognized as relating to embolization. Thepresent invention is intended to entrap and remove emboli in a varietyof situations. For example, in accordance with one aspect of theinvention, blood may be filtered in a patient during procedures whichaffect blood vessels of the patient. The present invention isparticularly suited for temporary filtration of blood in an artery of apatient to entrap embolic debris. This in turn will eliminate or reduceneurologic, cognitive, and cardiac complications helping to reducelength of hospital stay. In accordance with another aspect of theinvention, blood may be filtered temporarily in a patient who has beenidentified as being at risk for embolization.

As for the devices, one object is to provide simple, safe and reliabledevices that are easy to manufacture and use. A further object is toprovide devices that may be used in any blood vessel. Yet another objectis to provide devices that will improve surgery by lesseningcomplications, decreasing the length of patients' hospital stays andlowering costs associated with the surgery. See Barbut et al.,"Intraoperative Embolization Affects Neurologic and Cardiac Outcome andLength of Hospital Stay in Patients Undergoing Coronary Bypass Surgery,"Stroke (1996).

The devices disclosed herein have the following characteristics: canwithstand high arterial blood flow rates for an extended time; include amesh that is porous enough to allow adequate blood flow in a bloodvessel while capturing mobile emboli; can be used with or withoutimaging equipment; remove the entrapped emboli when the operation hasended; will not dislodge mobile plaque; and can be used in men, women,and children of varying sizes.

As for methods of use, an object is to provide temporary filtration inany blood vessel and more particularly in any artery. A further objectis to provide a method for temporarily filtering blood in an aorta of apatient before the blood reaches the carotid arteries and the distalaorta. A further object is to provide a method for filtering blood inpatients who have been identified as being at risk for embolization. Yeta further object is to provide a method to be carried out in conjunctionwith a blood filter device and visualization technique that will assista user in determining appropriate sites of filtration. Thisvisualization technique also may assist the user in adjusting the bloodfilter device to ensure effective filtration. Yet a further object is toprovide a method for filtering blood during surgery only when filtrationis necessary. Yet another object is to provide a method for eliminatingor minimizing embolization resulting from a procedure on a patient'sblood vessel by using a visualization technique to determine anappropriate site to perform the procedure. Another object is to providea method for minimizing incidence of thromboatheroembolisms resultingfrom cannula procedures by coordinating filtration and blood flowdiffusion techniques in a single device. Another object is to provide amethod of passing a filtering device through a vessel wall by firstcapturing the mesh filter with a sleeve so as to reduce the deviceprofile. For a related discussion of subject matter pertaining to afilter cannula, the reader is referred to co-pending U.S. applicationSer. No. 08/640,015, filed Apr. 30, 1996, U.S. application Ser. No.08/584,759, filed Jan. 9, 1996, U.S. application Ser. No. 08/580,223,filed Dec. 28, 1995, and U.S. application Ser. No. 08/553,137, filedNov. 7, 1995, all of which are expressly incorporated herein byreference in their entirety.

BRIEF DESCRIPTION OF DRAWINGS

Reference is next made to a brief description of the drawings, which areintended to illustrate blood filter devices for use herein. The drawingsand detailed description which follow are intended to be merelyillustrative and are not intended to limit the scope of the invention asset forth in the appended claims.

FIG. 1 is a longitudinal view of a blood filter device according to oneembodiment.

FIG. 2 is a longitudinal view of a blood filter device according toanother embodiment, and in which the device is unsheathed and in anactuation position.

FIG. 3 is a longitudinal view of a blood filter device depicted in FIG.2, and in which the device is unsheathed and in a release position.

FIG. 4 is a longitudinal view of a blood filter device according toanother embodiment.

FIG. 5 is a cross-sectional view through section line 5--5 of the devicedepicted in FIG. 4, showing the connection between the balloon and meshof the device.

FIG. 6 is a longitudinal view of a blood filter device according toanother embodiment, showing the filter contracted before deployment andcontained under a retracting handle.

FIG. 7 is a longitudinal view of the blood filter device depicted inFIG. 6, showing the filter deployed after insertion of the cannula intothe aorta.

FIG. 8 is a longitudinal view of a flexible arterial cannula showingstandard features which are presently commercially available.

FIG. 9 is a longitudinal view of a blood filter device according toanother embodiment, showing the filter deployed after insertion of thecannula into the aorta.

FIG. 10 is a longitudinal view of a blood filter device according toanother embodiment.

FIG. 10A is a cross-sectional view through section line A--A of theblood filter device depicted in FIG. 10.

FIG. 11 is longitudinal view of a cannula with associated filter anddistal flow diffuser.

FIG. 11a is a detail of the flow diffuser of FIG. 11.

FIG. 12 is a longitudinal view of a cannula with associated filter anddistal flow diffuser.

FIG. 12a is a detail of the flow diffuser of FIG. 12.

FIG. 13 is a longitudinal view of a cannula with associated filter andproximal flow diffuser.

FIG. 14 is a longitudinal view of a cannula with associated filter and aproximal flow diffuser.

FIG. 15 is a longitudinal view of a cannula with associated filteraccording to another embodiment wherein the cannula includes acondom-like filter sleeve shown in a rolled back position.

FIG. 16 is a longitudinal view of the cannula with associated filter ofFIG. 15 wherein the unrolled filter sleeve has captured the filterassembly.

FIG. 17 shows detail of an unrolled filter sleeve and accompanyingcontrol lines.

FIG. 18 is a three-dimensional drawing of a cannula with associatedfilter with a filter sleeve in the rolled up position.

FIG. 19 is a longitudinal view of a cannula with associated filterincluding a sleeve deployable by virtue of a pulley mechanism.

FIG. 20 is a longitudinal view of a cannula with associated filterwherein the cannula has a collapsible section which can accommodate thethickness of the filter.

FIG. 21 is a longitudinal view of a balloon aortic elastic cannulawherein the cannula's outer diameter and filter profile are reduced byintroduction of a stylet in the cannula's central lumen.

FIG. 22 is a longitudinal view of the balloon aortic elastic cannula ofFIG. 21 wherein the stylet has been withdrawn.

FIG. 23 is a longitudinal view of a cannula wherein the expander isproximal to the collapsible portion of the distal cannula.

FIG. 24 is a longitudinal view of a cannula wherein the expander hasbeen inserted into the collapsible portion of the distal cannula.

FIGS. 25 and 25c depict a cannula wherein the filter has an elasticmericcompliant edge which conforms to vessel irregularities.

FIGS. 25a, 25b, and 25d show other views of the cannula depicted in FIG.25c.

FIG. 26 shows a cannula having an open-ended sleeve disposed within theaorta.

DETAILED DESCRIPTION

Referring more particularly to the drawings, FIG. 1 shows one embodimentof the blood filter device for use herein. The blood filter device 10comprises an insertion tube 20, an umbrella frame 30, and an end plate60, an activation tube 50, a mesh 40, an adjustment device 70, and ahandle 80.

The device 10 is introduced into a vessel through a main port 7 of acannula 5, and blood or other surgical equipment may be introduced intothe main port 7 of the cannula 5 through a side port 3. The cannula 5and the device 10 will not interfere with placement of equipment whichmay be used during a surgical procedure.

As shown in FIG. 1, the umbrella frame 30 comprises a plurality of arms32 (some of which are not shown), which may include 3 arms, morepreferably 4 arms, more preferably 5 arms, more preferably 6 arms, morepreferably 7 arms, more preferably 8 arms, more preferably 9 arms, andmost preferably 10 arms. The arms are sonically welded to a socket 34,which in turn is adhesive bonded to the insertion tube 20 which isdimensioned to fit within the main port 7 of the cannula 5 withoutunnecessarily impeding blood flow. Alternatively, the socket 34 may beconnected to the insertion tube 20 by welding or epoxy. The insertiontube 20 is made of commercially available material such as polyvinyl,clear PVC, polyurethane, or other plastics. The arms 32 of the umbrellaframe 30 are made of plastic or thin gage metal. Because of theflexibility of this material, the arms 32 bend without the need forextra parts such as hinges. This simplifies assembly and reduces thechances of misassembly. Each of the arms 32 is provided with an undercutto facilitate bending. Alternatively, the arms 32 may be made of amaterial having a shape memory characteristic, causing the arms to bendin the absence of external forces. A silicone material may be attachedto the arms at the point at which they bend to act as a shock absorber.Alternatively, the arms may be coated with a hydrophilic coating orother shock absorbing material. Although the frame includes eight armsin one preferred embodiment, it is also contemplated that the umbrellaframe may comprise more or less than eight arms.

The end plate 60 comprises a one-piece injection molded component, madeof plastics or metal. The end plate 60 is substantially O-shaped with aradius r and indent in the center of the O-shape. The eight arms 32 ofthe umbrella frame 30 are sonic welded or bonded to the end plate 60 ateight arm junctures 61 spaced in 45 degree increments along acircumference of a circle defined by radius less than r. The activationtube 50 is welded or attached with epoxy to the indent 62.

The activation tube 50 extends from the end plate 60, through theinsertion tube 20, to the adjustment device 70 housed in the handle 80as shown in FIG. 1. The adjustment device 70 is a linear actuationdevice, comprising a thumb switch 72 which is attached to a guide frame74 which in turn is attached to the activation tube 50 via a bond joint.Thumb switch 72 comprises a base 76 and a ratchet arm 78 which movesalong a ratchet slot 82 along the top of the handle 80, locking inpredetermined intervals in a manner known in the art. Sliding the thumbswitch 72 away from the distal end 2 of the cannula 5 retracts theactivation tube 50, which in turn draws the end plate 60 toward thehandle 80. This causes the arms 32 of the umbrella frame 30 to bend andthe mesh 40 to open and ready to trap foreign matter in the blood.Sliding thumb switch 72 toward the distal end 2 of the cannula 5 pushesthe activation tube 50 in the direction of the mesh 40. The activationtube 50 then pushes the end plate 60 away from the handle 80, causingthe arms 32 of the umbrella frame 30 to straighten and the mesh 40 toclose.

If, in the alternative, the arms 32 of the umbrella frame 30 are made ofa material with a shape memory characteristic, the linear actuationdevice must include a locking mechanism which, when locked, maintainsthe arms 32 in a straight position and which, when released, allows thearms 32 of the umbrella frame 30 to bend.

Other linear actuation devices known in the art also may be incorporatedinto the present invention such as, but not limited to, a friction fitslot device with a nub on the end, a device which incorporates hydraulicpressure or an electromechanical device with a motor.

To filter blood effectively, i.e., to entrap embolic material, withoutunduly disrupting blood flow, the mesh must have the appropriatephysical characteristics, including area (A_(M)), thread diameter(D_(T)), and pore size (S_(P)). In the aorta, the mesh 40 must permitflow rates as high as 3 L/min or more, more preferably 3.5 L/min ormore, more preferably 4 L/min or more, more preferably 4.5 L/min ormore, more preferably further 5 L/min or more preferably 5.5 L/min ormore, and most preferably 6 L/min or more at pre-arterial pressures ofaround 120 mm Hg or less.

In order to entrap as many particles as possible, mesh with theappropriate pore size must be chosen. The dimensions of the particles tobe entrapped are an important factor in this choice. In the aorta, forexample, particle size has been found to range from 0.27 to 2.88 mm.with a mean of 0.85 mm, and particle volume has been found to range from0.01 to 12.45 mm³, with a mean of 0.32 mm³. Approximately 27 percent ofthe particles have been found to measure 0.6 mm or less in diameter.During cardiac bypass surgery in particular, aortic embolic load hasbeen found to range from 0.57 cc to 11.2 cc, with a mean of 3.7 cc, andan estimated cerebral embolic load has been found to range from 60 to510 mm³, with a mean of 276 mm³.

When a bubble greater than 100 μm diameter encounters the filter, theremust be sufficient pressure on the proximal side of the filter to forcethe bubble through the pore. The surface tension of the blood generallyprevents the bubble from deforming and extruding through the pore, butrather the bubble breaks apart into a plurality of bubbles small enoughto pass freely through the pore. The filter thereby acts as a bubblesieve.

The benefit of reducing the size of the interactive bubbles is twofold.First, the potential of a bubble to cause ischemia is directly relatedto its diameter. The larger the bubble, the more likely it is to blockblood flow to a larger area of the brain. Smaller bubbles may blocksmaller arteries, but will have less overall ischemic effect. Second,smaller bubbles will be absorbed into tissue and cells more quickly thanlarge bubbles, because of their greater surface area to volume ratio.The net effect is smaller bubbles which may make their way into thebrain, and bubbles which will be more quickly metabolized furtherreducing risk of embolic ischemia.

Another method by which large bubbles can be rendered into smallerbubbles is due to velocity and momentum effects. During moments of peaksystolic cardiac output, the blood velocity from the heart is at itsmaximum (100-150 cm/s). If a bubble is trapped against the intra-aorticfilter and is subject to instantaneous high velocity blood flow, themomentum of the blood on the bubble will cause the bubble to shatterinto smaller bubbles. The smaller bubbles will then "escape" through thepores in the filter if they have been rendered small enough.

By way of example, when a device of the present invention is intendedfor use in the aorta, the area of the mesh required for the device 10 iscalculated in the following manner. First, the number of pores N_(P) inthe mesh is calculated as a function of thread diameter, pore size, flowrate, upstream pressure and downstream pressure. This is done usingBernoulli's equation for flow in a tube with an obstruction: ##EQU1##

In this equation, P is pressure, p is density of the fluid, g is thegravity constant (9.8 m/s²), V is velocity, K represents the lossconstants, and f is the friction factor. The numbers 1 and 2 denoteconditions upstream and downstream, respectively, of the filter.

The following values are chosen to simulate conditions within the aorta:

P₁ =120 mm Hg;

P₂ =80 mm Hg;

K_(entry) =0.5;

K_(exit) =1.0;

K=K_(entry) +K_(exit) ; and ##EQU2## is 30. Assuming laminar flow out ofthe mesh filter, f is given as ##EQU3## where Re is the Reynold's numberand the Reynold's number is given by the following equation: ##EQU4##where μ is the kinematic viscosity of the fluid and A_(h) is the area ofone hole in the mesh given by S_(P) *S_(P).

Conservation of the volume dictates the following equation: ##EQU5##where Q is the flow rate of the blood. In addition, V₁ is given by:##EQU6## where A_(vessel) is the cross-sectional area of the vessel.Substitution and manipulation of the above equations yields N_(P).

Next, the area of the mesh is calculated as a function of the number ofpores, thread diameter and pore size using the following equation:

    A.sub.M =N.sub.P *(D.sub.T +S.sub.P).sup.2

In an embodiment of the device 10 that is to be used in the aorta, meshwith dimensions within the following ranges is desirable: mesh area is3-10 in², more preferably 4-9 in², more preferably 5-8 in², morepreferably 6-8 in², most preferably 7-8 in² ; mesh thickness is 20-280μm, more preferably 23-240 μm, more preferably 26-200 μm, morepreferably 29-160 μm, more preferably 32-120 μm, more preferably 36-90μm, more preferably 40-60 μm; thread diameter is 10-145 μm, morepreferably 12-125 μm, more preferably 14-105 μm, more preferably 16-85μm, more preferably 20-40 μm; and pore size is 50-300 μm, morepreferably 57-285 μm, more preferably 64-270 μm, more preferably 71-255μm, more preferably 78-240 μm, more preferably 85-225 μm, morepreferably 92-210 μm, more preferably 99-195 μm, more preferably 106-180μm, more preferably 103-165 μm, more preferably 120-150 μm. In apreferred embodiment of the invention, mesh area is 3-8 in², meshthickness is 36-90 μm, thread diameter is 16-85 μm, and pore size is103-165 μm. In a further preferred embodiment of the invention, mesharea is 3-5 in², mesh thickness is 40-60 μm, thread diameter is 20-40μm, and pore size is 120-150 μm.

The calculation set forth above has been made with reference to theaorta. It will be understood, however, that blood flow parameters withinany vessel other than the aorta may be inserted into the equations setforth above to calculate the mesh area required for a blood filterdevice adapted for that vessel.

To test the mesh under conditions simulating the conditions within thebody, fluid flow may be observed from a reservoir through a pipeattached to the bottom of the reservoir with the mesh placed over themouth of the pipe through which the fluid exits the pipe. A mixture ofglycerin and water may be used to simulate blood. Fluid height (h) isthe length of the pipe in addition to the depth of the fluid in thereservoir, and it is given by the following equation: ##EQU7## where ρis given by the density of the glycerin-water mixture, and g is given bythe gravity constant (9.8 ms²).

Bernoulli's equation (as set forth above) may be solved in order todetermine (D_(T) /S_(P))_(Equiv). V₁ is given by the following equation:##EQU8## where Q is the flow rate which would be measured during testingand A₁ is the cross-sectional area of the pipe. V₂ is given by thefollowing equation: ##EQU9## where N is the number of pores in the meshand A₂ is the area of one pore. Further, P₁ =120 mm Hg and P₂ =0 mm Hgand S_(P) is the diagonal length of the pore. Reynold's number (Re) isgiven by the following equation: ##EQU10## where ρ and μ are,respectively, the density and kinematic viscosity of the glycerin-watermixture.

Once appropriate physical characteristics are determined, suitable meshcan be found among standard meshes known in the art. For example,polyurethane meshes may be used, such as Saati and Tetko meshes. Theseare available in sheet form and can be easily cut and formed into adesired shape. In a preferred embodiment, the mesh is sonic welded intoa cone shape. Other meshes known in the art, which have the desiredphysical characteristics, are also suitable. The mesh 40 is sonic weldedor adhesive bonded to the arms 32 of he umbrella frame 30 from the endplate 60 to a point on each arm 32 between the end plate 60 and thesocket 34 as shown in FIG. 1. This is the optimal placement of the Mesh40 when the device 10 is inserted into the vessel in the direction ofthe blood flow. However, it is also contemplated that the device 10 maybe inserted in a direction opposite the blood flow. In this case, themesh 40 would be attached to the arms 32 of the umbrella frame 30 fromthe socket 34 to a point on each arm 32 between the socket 34 and theend plate 60.

Anticoagulants, such as heparin and heparinoids, may be applied to themesh 40 to reduce the chances of blood clotting on the mesh 40.Anticoagulants other than heparinoids also may be used. Theanticoagulant may be painted or sprayed onto the mesh. A chemical dipcomprising the anticoagulant also may be used. Other methods known inthe art for applying chemicals to mesh may be used.

The device 10 may be used in the following manner. A cannula 5 isintroduced into the vessel through an incision made in the vessel wall,and the cannula 5 is then sutured to the vessel wall. The cannula 5 ispreferably size 22-25 French (outer diameter). The blood filter device10 is then inserted into the vessel through the cannula 5. Within thecannula 5, the blood filter device 10 is maintained in a releaseposition in which the arms 32 of the umbrella frame 30 are straight andthe mesh 40 is closed. (See FIG. 3.)

In order to actuate the device 10, the surgeon slides the thumb switch72 of the adjustment device 70 along the ratchet slot 82, away from thedistal end 2 of the cannula 5, until an appropriate actuation positionis achieved or until the mesh 40 is opened to its maximum size. (SeeFIG. 2.) The arms 32 may bend to varying degrees in a plurality ofactuation positions, and the appropriate actuation position depends onthe cross-sectional dimension of the blood vessel. During filtration, auser may gently palpate the outside of the blood vessel to feel pointsof contact between the vessel wall and the device 10. This enables theuser to determine the appropriate actuation position and the location ofthe device within the vessel.

When filtration has been completed, the user slides the thumb switch 72toward the distal end 2 of the cannula 5, thereby effecting the releaseposition, in which the arms 32 of the umbrella frame 30 straighten andthe mesh 40 closes around the captured emboli. (See FIG. 3.) The handle80 may be additionally provided with a marker band which matches up witha corresponding marker band on the thumb switch 72 when the device 10 isin the release position. The device 10 is pulled back into the cannula5, and then cannula 5 and the device 10, along with the captured emboli,are removed from the body.

In another embodiment, a blood filter device is provided as illustratedin FIGS. 2 and 3. The device 10 comprises an introducer 103, a cannula105, having a distal end 111, a sheath 120, an umbrella frame 130, anannular mesh 140, a movable ring 150, a fixed ring 160, guidewires 170,and a clam-shell handle 180.

The introducer 103 comprises a cylinder 107 and an adjustable suturering 109. The cylinder 107 of the introducer 103 is made to fit aroundthe sheath 120, which slides over the cannula 105 and the guidewires170.

The umbrella frame 130 is substantially similar to the umbrella frame 30depicted in FIG. 1. The umbrella frame 130 comprises a plurality of arms132 (some of which are not shown) as discussed above with reference toFIG. 1, which arms are connected at one end (of each arm 132) to thefixed ring 160 and at the other end (of each arm 132) to the movablering 150. The fixed ring 160 is firmly secured to the cannula 105. Eachguidewire 170 is firmly secured at one end to the movable ring 150m,which slides along the outer surface of the cannula 105, and at theother end to the clamshell handle 180, which is a linear actuationdevice known in the art.

The mesh 140 must entrap embolic material without unduly disruptingblood flow. This mesh 140 also may be found among standard meshes knownin the art. The same analysis used to select and test the mesh 40 of thefirst preferred embodiment may be used to select the mesh 140.

The device 10 is used in the following manner. The device 10 is insertedinto the blood vessel. The sheath 120 is retracted until it exposes theumbrella frame 130. A user effects the actuation position by pushing themovable ring 150 toward the fixed ring 160 via the clam-shell handle 180and the guidewires 170 as shown in FIG. 2. In the actuation position,the arms 132 of the umbrella frame 130 are bent and the annular mesh 140is open and ready to capture foreign matter in the blood.

In order to remove the blood filter 10 from the body, the user firstpulls the movable ring 150 away from the fixed ring 160 via theclamshell handle 180 and the guidewires 170. This causes the arms 132 ofthe umbrella frame 130 to straighten and the annular mesh 140 to close,trapping the emboli against the cannula 105. The user then removes theblood filter device 10 from the body along with the captured emboli.Alternatively, the user may first slide the sheath 120 back over thecannula 105, and then remove the device 10 from the body along with thecaptured emboli.

In an alternative embodiment adapted for use in the aorta during cardiacsurgery, a second mesh may be placed over the distal end 111 of thecannula 105 or within the cannula 105 so that blood flowing into thebody from an extracorporeal source is also filtered. Alternatively, inlieu of an annular mesh 140 and a second mesh, a single mesh may be usedwhich is configured such that it covers the distal end 111 of thecannula 105.

An advantage of the embodiment depicted in FIG. 2 is that it does notrequire a cannula with a separate port for the introduction of blood ora surgical equipment.

FIG. 4 shows another embodiment of the blood filter device disclosedherein. As shown in FIG. 4, the blood filter device 10 comprises a mesh220, an inflatable balloon 230, a collar 240, a plurality of tie lines250, and an actuation assembly 260. The mesh 220 is attached to theballoon 230 via the collar 240. In use, the device 10 is positioned andmaintained in a blood vessel via the plurality of tie lines 250.Manipulation of actuation assembly 260 inflates and deflates the balloon230 and controls the degree of inflation and deflation. Inflation of theballoon 230 opens the mesh 220, and deflation of the balloon 230 allowsthe mesh 220 to close.

Mesh 220, found among standard meshes as in the first two embodiments,should cover substantially all of the cross-sectional area of a vesselso that blood flowing in the vessel must pass through the mesh 220. Inthis way, foreign matter in blood within the vessel is entrapped by themesh 220. In the preferred embodiment, the mesh 220 is generallycone-shaped. However, the shape of the mesh 220 may be modified toassume any shape as long as blood flowing in the vessel passes throughthe mesh 220.

As shown in FIG. 4, inflatable balloon 230 is attached to the mesh 220via the collar 240. In a preferred embodiment, the balloon 230 is madeof two pieces of a flexible, slightly porous material such as urethaneor polyethylene terephalate (PET), each piece having an outer diameterand an inner diameter. These pieces are welded together at both theouter and inner diameters in a manner known in the art. The balloon 230also has a valve 268 and a valve stem 266 located between the outerdiameter and the inner diameter of the balloon 230. Material used forthe balloon 230 must be capable of inflation and deflation. It also mustbe sufficiently flexible to conform to the walls of a vessel regardlessof possible irregularities in the walls, such as may be caused by plaqueor other materials adhering to the walls. Material used for the balloon230 also must be sufficiently flexible to allow the balloon 230 to foldup within a cannula 205. Exemplary materials include elastomeric andcertain non-elastomeric balloons.

To inflate the balloon 230 and thereby open the mesh 220, a fluid or agas, is introduced into the balloon 230 through the valve 268. Todeflate the balloon 230, the fluid or gas is removed from the balloon230 through the valve 268. Fluids such as saline may be used, and gasessuch as inert gases may be used with this invention. Any fluid or gasmay be used as long as it does not harm the patient if released into thebloodstream. The saline or other suitable inflation material istypically stored in a reservoir outside the body, which is capable offluid communication with the balloon 230 through a tube 264.

In an embodiment of the devices suited for placement in the aorta, theballoon 230 has an outer diameter of approximately 100 Fr., morepreferably 105 Fr., more preferably 110 Fr., more preferably 115 Fr.,more preferably 120 Fr., and most preferably 125 Fr., or greater, and aninner diameter of approximately 45 Fr. (1 Fr.=0.13 in.) when fullyinflated. The dimensions of the balloon 230 may be adjusted inalternative embodiments adapted for use in vessels other than the aorta.Alternatively, expandable members other than a balloon also may be usedwith this invention.

Referring to FIG. 4, the collar 240 is attached to the outer diameter ofthe balloon 230 and is a generally circular piece of plastic. Othermaterials, such as silicone or high density polyethylene may be used.This material should be rigid enough to withstand flow conditions inblood vessels, yet flexible enough to expand as the balloon 230 isinflated and to fold up as the balloon 230 is deflated and stored withinthe cannula 205. The collar 240 has both an inner and outer diameter,and the outer diameter is bent slightly outward. As shown in FIG. 5, thecollar 240 is attached to the outer diameter of the balloon 230 bywelding, adhesive or other attachment means known in the art. The mesh220, in turn, is adhesive bonded to the collar 240. Alternatively, themesh 220 may be connected to the collar 240 by welding, epoxy, or othersuitable adhesive means.

Actuation of the device 10 is accomplished by the actuation assembly260, which inflates and deflates the balloon 230 by introducing into andremoving from the balloon 230 the fluid or gas. The actuation assembly260 also controls the degree to which the mesh is opened within theblood vessel. The actuation assembly 260 may be used to adjust the fitof the device 10 within the vessel during filtration or use of thedevice 10. In addition, because the degree to which the mesh is openedmay be adjusted by the actuation assembly 260, one embodiment of thedevice may be suitable for a variety of vessel sizes.

Actuation assembly 260 comprises an inflation catheter 262 and the tube264 which is connected to the valve stem 266. The inflation catheter 262is preferably 9 F. O.D. and is marked in cubic centimeter increments inorder to monitor the degree to which the balloon 230 is inflated. Thetube 264 is preferably size 12 Fr. O.D. and 7.2 Fr. I.D.

A plurality of tie lines 250, which may include three tie lines, fourtie lines, or more than four tie lines, position and maintain the device10 in place in the bloodstream. The tie lines 250 are made of wire andare threaded through the balloon 230 at points equally spaced along theinner diameter of the balloon, e.g., for four tie lines the four pointsare space 90 degrees apart along the inner diameter of the balloon 230.The tie lines 250 may be made of other materials having sufficientstiffness to push and pull the balloon 230 out of and into the cannula205 and to maintain the device 10 within the blood vessel.

All components of this device should be composed of materials suitablefor insertion into the body. Additionally, sizes of all components aredetermined by dimensional parameters of the vessels in which the devicesare intended to be used. These parameters are known by those skilled inthe art.

By way of purely illustrative example, the operational characteristicsof a filter according to the invention and adapted for use in the aortaare as follows:

    ______________________________________                                        Temperature Range                                                                           25-39 degrees C.                                                Pressure Range                                                                              50-120 mm Hg                                                    Flow Rate     usually up to 5 L/min., can be as high as 6                                   L/min.                                                          Duration of single use                                                                      up to approximately 5 hours                                     Average emboli trapped                                                                      5-10,000                                                        Pressure gradient range                                                                     (100-140)/(50-90)                                               ______________________________________                                    

Modification of the operational characteristics set forth above for useof the present invention in vessels other than the aorta are readilyascertainable by those skilled in the art in view of the presentdisclosure.

An advantage of all embodiments disclosed herein is that the bloodfilter will capture emboli which may result from the incision throughwhich the blood filter is inserted.

In use, there are a number of methods for protecting patients fromembolization and for filtering blood using the devices disclosed herein.Temporary filtration is frequently required in association withprocedures performed on blood vessels because there is a possibility ofembolization associated with such procedures. For example, there is acorrelation between embolization and the aortic clamping and unclampingwhich is performed during cardiac bypass surgery.

The devices of the present invention are particularly suited for use inmethods of the present invention. However, other devices may be adaptedfor use in accordance with the methods of the present invention.

The methods of the present invention generally include the followingsteps: introducing a blood filter device into a blood vessel of apatient to entrap embolic matter or foreign matter in the blood; andremoving the mesh and the entrapped foreign matter from the bloodvessel. The blood filter device also may be adjusted if this isnecessary during the course of filtration.

In addition, use of visualization techniques is also contemplated inorder to determine which patients require filtration (identify riskfactors), where to effectively position a blood filter device tomaximize effectiveness, when to adjust the device if adjustment isnecessary, when to actuate the device and appropriate regions forperforming any procedures required on a patient's blood vessel.

According to one method of the present invention, the blood filterdevice depicted in FIGS. 4 and 5 is introduced into a patient's bloodvessel. Typically, an incision is first made in a vessel of a patient,and, with reference to FIG. 4, cannula 205 is introduced into theincision in the direction of blood flow. Within the cannula 205, thedevice 10 is stored in a closed position in which the balloon isdeflated and generally folded in upon itself and the mesh 220 is closed.

The blood filter device 10 is then pushed out through the cannula 205into the vessel by pushing the tie lines 250 in the direction of bloodflow. To actuate the device 10, the actuation assembly 260 inflates theballoon until the balloon 230 opens the mesh 220 within the vessel tocover substantially all of the cross-sectional area of the vessel suchthat blood flowing through the vessel flows through the mesh 220. As theblood flows through the mesh 220, foreign matter is entrapped by themesh.

When the filter is no longer needed, the device 10 is removed from thevessel along with the entrapped foreign matter. The balloon 230 isdeflated, and the tie lines 250 are pulled toward the cannula oppositethe direction of the blood flow. As the balloon 230 is pulled into thecannula 205, the balloon 230 folds in upon itself, and the mesh 220closes around the entrapped foreign matter. In an alternativeembodiment, the cannula 205 may be configured to further accommodateentry of the balloon 230, the mesh 220, and the entrapped foreign matterinto the cannula 205 without disturbing blood flow. For example, the endof the cannula placed within the vessel may be very slightly flared.

In accordance with one aspect of the invention, a visualizationtechnique, such as TCD, is used to determine when to actuate a bloodfilter device. For example, during cardiac bypass surgery, flurries ofemboli are detected during aortic cannulation, inception, andtermination of bypass and cross-clamping of the aorta. Therefore, a meshmay be opened within a vessel downstream of the aorta during theseprocedures and closed when embolization resulting from these procedureshas ceased. Closing the mesh when filtration is not required helps tominimize obstruction of the blood flow.

According to another embodiment, a visualization technique is used tomonitor emboli entering cerebral circulation to evaluate theeffectiveness of a blood filter device in trapping emboli. Also, avisualization technique is useful to positioning a device within avessel so that it operates at optimum efficiency. For example, a usermay adjust the position of the device if TCD monitoring indicates emboliare freely entering the cerebral circulation. In addition, a user mayadjust a mesh of a blood filter device to ensure that substantially allof the blood flowing in the vessel passes through the mesh.

According to yet another embodiment, a visualization technique, such asTEE and epicardial aortic ultrasonography, is used to identify thosepatients requiring blood filtration according to the present invention.For example, these visualization techniques may be used to identifypatients who are likely to experience embolization due to the presenceof mobile plaque. These techniques may be used before the patientundergoes any type of procedure which will affect a blood vessel inwhich mobile plaque is located.

Additionally, visualization techniques may be used to select appropriatesites on a blood vessel to perform certain procedures to eliminate orreduce the occurrence of embolization. For example, during cardiacbypass surgery, the aorta is both clamped and cannulated. Theseprocedures frequently dislodge atheromatous material already present onthe walls of the aorta. To minimize the amount of atheromatous materialdislodged, a user may clamp or cannulate a section of the aorta whichcontains the least amount of atheromatous material, as identified byTEE, epicardial aortic ultrasonography or other visualization technique.

Procedures other than incising and clamping also tend to dislodgeatheromatous material from the walls of vessels. These proceduresinclude, but are not limited to, dilatation, angioplasty, andatherectomy.

Visualization techniques also may be used to select appropriate sitesfor filtering blood. Once atheromatous material is located within avessel, a blood filter device may be placed downstream of that location.

Visualization techniques, other than those already mentioned, as areknown to those skilled in the art, are also useful in ascertaining thecontours of a blood vessel affected by surgical procedure to assess avariety of risk of embolization factors, and to locate appropriatesections of a vessel for performing certain procedures. Any suitablevisualization device may be used to evaluate the efficacy of a device,such as those disclosed herein, in trapping emboli.

In another embodiment, a cannula with associated filter is provided asdepicted in FIGS. 6 and 7. With reference to FIG. 6, the device includesa pressurizing cannula 300 having proximal region 301, distal region302, and an intermediate region which connects the proximal and distalregions. The pressurizing cannula 300 is typically a rigid orsemi-rigid, preferably transparent tube having a first substantiallycylindrical lumen 303 which extends from the proximal region to thedistal region and is shaped to receive blood supply cannula 350. Thepressurizing cannula 300 further includes at its proximal region luerfittings 304 and 305 which are shaped to receive a cap or septum 306 anda syringe 307 filled with saline or gas and having a locking mechanism308 (FIG. 7) for locking the barrel 309 and plunger 310 in a fixedposition. The pressurizing cannula 300 typically has a dual lumen toeffect pressurization of the inflation seal (discussed below). Thus luer305 is connected to passage 311 which is in fluid communication with asecond lumen 312 which extends from the proximal to the distal end ofpressurizing cannula 300. Meanwhile, luer 304 is connected to passage313 which is in fluid communication with a third lumen 314 which extendsfrom the proximal to the distal end of pressurizing cannula 300. At itsdistal region, the pressurizing cannula 300 includes a blood filtrationassembly 315 which is shown in greater detail in FIG. 7.

FIG. 8 depicts a standard flexible arterial cannula 400 which iscommercially available from Sarns 3M (Ann Arbor, Mich.). With referenceto FIG. 8, the cannula will typically have a length of about 25 cm. Thecannula includes a distal end region 401, a proximal end region 402, andan intermediate region disposed therebetween. Distal end region 401 hasan outer diameter of about 8 mm, and a sealing ring 403 having anenlarged diameter of about 13 mm, a width of about 5 mm, and beingdisposed about 25 mm from the distal tip of cannula 400. Sealing ring403 functions as an anchor point against the inside of an aorticincision so that cannula 400 does not slide from the aorta during aprocedure. Proximal end region 402 includes a connector 404 which joinsthe cannula to the blood machine. At its proximal tip, the cannulaincludes a tapered joint 405 which connects and locks the cannula to abypass-oxygenator machine.

Referring again to FIG. 6, blood supply cannula 350 may have certainfeatures in common with the standard cannula 400 depicted in FIG. 8.Blood supply cannula 350 for use herein is a substantially cylindrical,semi-rigid, and preferably transparent tube which includes a rib 351disposed about the circumference at a distal region thereof. The bloodcannula is slideable within the pressurizing cannula, and in theproximal region, the blood cannula 350 may be angled to adopt a shapewhich does not interfere with syringe 307. Moreover, the blood cannulawill typically include a fitting or molded joint 352 which is adaptedfor coupling to a bypass-oxygenator system. Blood cannula 350 is adaptedto carry blood to the aorta from the bypass-oxygenator system.

The pressurizing cannula may also include an inserting and retractinghandle 380 comprising a substantially cylindrical tube disposed aboutthe intermediate region of pressurizing cannula 300. Handle 380 willgenerally include a rigid or semi-rigid, preferably transparent tubewith molded hand grip to facilitate holding and inserting. Withreference to FIG. 7, handle 380 is slideable relative to thepressurizing cannula 300, and may include a sealing member 381comprising a rubber washer or O-ring mounted in a proximal region of thehandle and disposed between handle 380 and pressurizing cannula 300 toprevent leakage of blood therebetween. Handle 380 may includecorrugation ribs 382 and its proximal and intermediate regions, and asubstantially flat or level collar insertion region 383 adapted to fittightly against vessel material at an aortic incision. In certainembodiments, the collar insertion region 383 will include a sealing ringor rib (not shown), having a width of about 5 mm and an outer diameterof about 13 mm, which serves as an anchor against the aorta to preventthe cannula assembly from slipping out during a surgical procedure. A"purse string" suture is generally tied around the circumference of theaortic incision, and this string will be tightened around the ring incollar region 383 to prevent slippage of the cannula assembly.

Handle 380 may also include an enlarged end region 384 which enclosesthe blood filtration assembly 315 as depicted before insertion in FIG.6. This housing enclosure 384 is a particularly preferred componentbecause it prevents inadvertent deployment of the blood filtrationassembly, and it provides a smooth outer surface to the cannula whichfacilitates entry through an incision in the aorta without tearing theaorta. In the absence of such housing enclosure, the balloon and filterare liable to scrape against the inner wall of a vessel, and therebydamage or rupture the vessel. At its distal end, handle 380 may includeinverted cuff 385 which bears against rib 351 of blood cannula 350 toform a seal when the filtration assembly 315 is enclosed in handle 380.

With reference to FIG. 7, the distal region of pressurizing cannula 300is shown with blood filtration assembly 315 deployed in the ascendingregion of a human aorta 399. Handle 380 has been moved proximally toexpose filter assembly 315. The distal region of pressurizing cannula300 includes a plurality of spokes or holding strings 316 made fromDacron™ or other suitable material. Holding strings 316 connect thedistal region of the pressurizing cannula 300 to an inflation seal 317which comprises a continuous ring of preferably thin tubing attached tofilter mesh 318 on its outer side. Filter mesh 318 is bonded at itsdistal end around the circumference of blood cannula 350, preferably ata cross-sectional position which closely abuts rib 351.

Inflation seal 317 may be constructed from elastomeric ornon-elastomeric tubular material which encloses donut-shaped chamber319. When deployed, the inflation seal will expand to a diameter whichfits tightly against the lumen of aorta 399. The inflation seal willthus be capable of expansion to an outer diameter of at least 2 cm, morepreferably at least 2.5 cm, more preferably at least 3 cm, morepreferably at least 3.5 cm, more preferably at least 4 cm, morepreferably at least 4.5 cm. These diameter ranges will accommodate bothpediatric use and adult use. The inflation seal is typically acontinuous ring of very thin tubing attached to the mesh filter on oneside and to the pressurizing cannula by holding strings on the otherside.

The inflation seal should be able to maintain an internal pressure inchamber 319, without bursting, of greater than 55 mm Hg, more preferablygreater than 60 mm Hg, more preferably greater than 70 mm Hg, morepreferably greater than 80 mm Hg, more preferably greater than 90 mm Hg,more preferably greater than 100 mm Hg, more preferably greater than 110mm Hg, more preferably greater than 120 mm Hg, more preferably greaterthan 130 mm Hg, more preferably greater than 140 mm Hg, more preferablygreater than 150 mm Hg. The internal pressure needed will depend on thepressure maintained in the aorta against the mesh. Thus, if the aorticpressure is 55 mm Hg, then the pressure in the inflation seal must begreater than 55 mm Hg to prevent leakage around the seal. Typically, theaortic pressure will be at least 75 mm Hg because this level of pressureis needed to ensure adequate brain perfusion. It will be recognized thatsuch inflation seal pressures are much higher than the maximum levelthat can be used in the pulmonary venous system because the veins andarteries therein will typically hold no more than about 40-50 mm Hg, orat most 60 mm Hg without rupture.

Chamber 319 is in fluid communication with a first tubular passage 320and a second tubular passage 321 which permit chamber 319 to be inflatedwith gas, or preferably a fluid such as saline. Passage 320 is in fluidcommunication with second lumen 312 of pressurizing cannula 300, whilepassage 321 is in fluid communication with third lumen 314 ofpressurizing cannula 300. Passage 320 and 321 thereby interconnectchamber 319 with the second and third lumens 312 and 314, respectively,of pressurizing cannula 300.

In certain embodiments, inflation seal 317 will include a septum 322which blocks the movement of fluid in one direction around chamber 319.If septum 322 is positioned in close proximity to the fluid entry port,then the injection of fluid will push all gas in chamber 319 aroundinflation seal 317 and out through passage 321. In one embodiment, theentry port and the exit port are positioned in close proximity withseptum 322 disposed between the entry and exit port. In this case,injection of fluid will force virtually all gas out of inflation seal317.

Filter mesh 318 is bonded at its proximal end to inflation seal 317 andat its distal end to blood cannula 350, optionally at the proximal ordistal edge of rib 351. Mesh 318 can be made of a material which isreinforced or non-reinforced. Mesh 318, when expanded as shown in FIG.7, may assume a substantially conical shape with a truncated distalregion. The mesh should be formed of a material having a pore size whichobstructs objects 5 mm in size or less, more preferably 3 mm in size,more preferably less than 3 mm, more preferably less than 2.75 mm, morepreferably less than 2.5 mm, more preferably less than 2.25 mm, morepreferably less than 2 mm, more preferably less than 1.5 mm, morepreferably less than 1 mm, more preferably less than 0.75 mm, morepreferably less than 0.5 mm, more preferably less than 0.25 mm, morepreferably less than 0.1 mm, more preferably less than 0.075 mm, morepreferably less than 0.05 mm, more preferably less than 0.025 mm, morepreferably 0.02 mm, and down to sizes just larger than a red blood cell.It will be understood that for a given pore size that blocks particlesof a certain size as stated above, that pore size will block allparticles larger than that size as well. It should also be understoodthat the necessary pore size is a function of blood throughput, surfacearea of the mesh, and the pressure on the proximal and distal side ofthe mesh. For example, if a throughput of 5-6 L/min. is desired at across-section of the aorta having a diameter of 40 mm, and a pressure of120 mm Hg will be applied to the proximal side of the mesh to obtain adistal pressure of 80 mm Hg, then a pore size of about 50 m is needed.By contrast, in the pulmonary artery the same throughput is needed, butthe artery cross-section has a diameter of only 30 mm. Moreover, theproximal pressure is typically 40-60 mm Hg, while the distal pressure isabout 20 mm Hg. Thus, a much larger pore size is needed to maintainblood flow. If pore sizes as disclosed herein for the aorta were used inthe pulmonary artery, the blood throughput would be insufficient tomaintain blood oxygenation, and the patient would suffer rightventricular overload because of pulmonary artery hypertension.

It will also be understood for this cannula apparatus that blood flow tothe patient is maintained by blood passage through blood cannula 350,and not through mesh 318. Thus, the cannula must have an inner diameterwhich allows blood throughput at a mean flow rate of at least 3.0L/min., more preferably 3.5 L/min., more preferably 4 L/min., morepreferably at least 4.5 L/min., more preferably at least 5 L/min., andmore. Of course, flow rate can vary intermittently down to as low as 0.5L/min. Therefore, the inner diameter of blood supply cannula 350 willtypically be at least 9 F (3.0 mm), more preferably 10 F, morepreferably 11 F, more preferably 12 F (4 mm), more preferably 13 F, morepreferably 14 F, more preferably 15 F (5 mm), and greater. Depending onthe inner diameter and thickness of the tubing, the outer diameter ofblood cannula 350 is approximately 8 mm. Meanwhile, the pressurizingcannula 300 and handle at the collar region 383 have outer diameters ofapproximately 10.5 mm and 13.0 mm, respectively. The foregoing rangesare intended only to illustrate typical device parameters anddimensions, and the actual parameters may obviously vary outside thestated ranges and numbers without departing from the basic principlesdisclosed herein.

In use, the cannula with associated filter has syringe 307 which isremoved, and aseptically filled with a saline solution. The syringe isthen attached to pressurizing cannula 300, and cap 306 is removed.Saline is injected until saline exits from luer 304, thereby purgingsubstantially all gas from the inflation seal and dual lumen system ofpressurizing cannula 300. Cap 306 is then replaced and secured to thepressurizing cannula 300.

Cardiac surgery can then be conducted in accordance with procedureswhich employ standard cannula insertion, as known in the art, anddiscussed more fully herein. The mesh 318 and inflation seal 317 areenclosed under handle 380 at the enlarged end, just beyond the distaltip of pressurizing cannula 300. The cannula is introduced into theaorta, preferably the ascending aorta, of a patient through an incision,and the incision may be tightened about the cannula by use of a "pursestring" suture. Cardiopulmonary bypass occurs through blood cannula 350.

With the cannula in place, the filter is ready for deployment. Thesurgeon grips the handle, and the blood cannula 350 and pressurizingcannula 300 are pushed forward. This movement breaks the seal at the tipof the handle and allows the blood cannula and pressurizing cannula tothrust forward, thereby releasing the filter. The plunger of the syringeis then depressed within the barrel to expand the inflation seal. Theinflation seal expands to ensure contact with the inside of the aorta atall points along the circumference of the lumen. The syringe is thenlocked in place to prevent inflation or depressurization of theinflation seal during use.

The aorta is then cross-clamped at a region between the heart and thecannula incision. Embolic material dislodged from the aorta is caughtand trapped by filter mesh 318. The bypass-oxygenator system is thenstarted to achieve cardiopulmonary bypass through blood cannula 350.Cardiac surgery is then performed while the filter and inflation sealare maintained in place for a number of hours, typically 8 hours orless, more typically 7 hours or less, more typically 6 hours or less,more typically 5 hours or less, more typically 4 hours or less, moretypically 3 hours or less, and more typically 2 hours or less.

At the end of the cardiac surgery, the filter is depressurized andremoved from the ascending aorta. The syringe lock is released and,while holding handle 380, the pressurizing cannula is drawn back. Thiswill cause release of saline from inflation seal 317, and will retrievethe filter mesh, inflation seal, and pressurizing cannula back into andunder the handle, as it was configured before deployment. Notably,embolic material collected in the filter is also trapped under thehandle at its enlarged segment. Optionally, the inflation seal may bedeflated before pull-back of the pressurizing cannula by operating thesyringe to withdraw saline from the inflation seal. Once the associatedfilter has been retrieved under the handle, the cannula can be removedfrom the patient without damaging the aortic incision by using standardprocedures.

In another embodiment, a cannula is provided as depicted in FIGS. 6 and7 with a continuous filter mesh as shown in FIG. 4 which extends beyondand over the lumen of the blood cannula so that blood from the cannulapasses through the mesh before circulating within the patient. Withreference to FIG. 9, the device may include a pressurizing cannula 300,blood cannula 350, inflation seal 317 and mesh 318. The device mayoptionally include a handle 380 and an inflation system as describedabove with reference to FIGS. 6 and 7. Moreover, the inflation systemmay be carried by either the pressurizing cannula or the blood cannula.In certain embodiments, the blood cannula and pressurizing cannula willbe integrally combined into a single unitary component, and theinflation system may be carried either within or on the outside of theblood cannula. It will be understood that FIG. 9 shares many features incommon with FIGS. 6 and 7, and the numbering of apparatus components hasbeen duplicated so that appropriate description can be found withreference to FIGS. 6 and 7.

In another embodiment, a cannula is provided with an inflatable loadingballoon as depicted in FIG. 10. The device includes cannula 421 havingpressurizing lumen 422 which extends from the proximal to the distalend. The cannula is equipped with an inflatable loading balloon 423which, when inflated, exerts a radial outward force on stiffening wireribs 424. The ribs support filtration mesh 425 which extends from thesurface of the cannula at one edge to inflation seal 426 at anotheredge. A plurality of retrieving strings 427 are optionally providedwhich are attached at another end (not shown) to the plunger of thepressurizing syringe and therefore can be activated (advanced andwithdrawn) by the motion of the pressurizing syringe which operates atthe proximal end of cannula 421. Alternatively, the strings may beattached at the proximal end to a ring or slide which can be drawn topull back, or advanced to let out the strings. FIG. 10A shows across-sectional view of aorta 399 taken through section line A--A. Itcan be seen that the cannula is equipped with a plurality of stiffeningwire ribs 424 which extend radially outward when loading balloon 423 isexpanded.

In another embodiment, a cannula with associated filter and distal flowdiffuser is provided in FIGS. 11 and 11a. With reference to FIGS. 11 and11a, the device includes a pressurizing cannula 300, blood supplycannula 350 and a blood filtration assembly 315 comprising holdingstrings 316 inflation seal 317, filter mesh 318, chamber 319, tubularpassages 320 and 321, and septum 322. As shown in FIG. 11a the distalend of the blood supply cannula is closed with a cap 390 and the flowdiffuser 395 is a rounded, hemispherical shape to facilitate theinsertion of the distal end of the cannula 350 into the vessel. The flowdiffuser 395 tapers towards the proximal end of the cannula 350 startingfrom the cap 390. The shape of the diffuser is preferably conical, inorder to avoid damaging the blood. However, other shapes, includingpyramidal shapes, may be employed.

In this FIGS. 11 and 11a embodiment, a plurality of outlet openings 391are formed in the sidewall of the cannula 350 adjacent to its distalend. The openings may have an arched configuration, with the curvedportion 392 of each arch oriented in the upstream direction. Althoughany number of openings are possible, a preferred embodiment has sixopenings. Preferably the total area of the openings is greater than thearea of the distal end opening of a conventional catheter of the samediameter. The length of the openings 391 are also preferably greaterthan the length of the flow diffuser 395.

In another embodiment, a cannula with associated filter and flowdiffuser is provided as depicted in FIGS. 12 and 12a. In thisembodiment, the distal end of the cannula 350 contains a diffuser 396with a helical configuration. The diffuser 396 can be held in placewithin the cannula by the tapering configuration of the distal end ofthe cannula, by adhesives, by ultrasonic welding, or by some othersuitable means. The diffuser is preferably formed from a flatrectangular member with a single one-hundred-eighty degree twist. Inthis embodiment, the distal end of the cannula is partially blocked.Additionally, any number of outlet openings 397 may be formed in thesidewall of the cannula.

The intra-cannula flow diffusers of FIG. 11 and FIG. 12 may also beemployed proximal to the filter by, for example, positioning thediffuser within the blood cannula of the device depicted in FIG. 9.Other variations and details of intra-lumen flow diffusers may be foundin Cosgrove et. al., Low Velocity Aortic Cannula, U.S. Pat. No.5,354,288, which is incorporated by reference herein.

In another embodiment, a blood cannula with associated filter and flowdiffuser is provided as in FIG. 13. In this embodiment the proximal endof a flow diffuser 702 is connected to the distal end of the cannula 350by a plurality of structural supports 704. The diffuser 702 ispreferably conical, although other shapes may be used. The distal end ofthe flow diffuser 702 extends to the apex of the filter 706 by virtue ofa linear shaft 708 said shaft running through the center of the expandedfilter. In this embodiment the flow diffuser 702 diffuses blood flowproximal to the filter 706.

In another embodiment, an arterial blood cannula is provided as in FIG.14. In this embodiment the flow diffuser 802 is contained within thedistal end of the blood cannula 10. In a preferred embodiment, thediffuser 802 is the helical diffuser shown in FIG. 12 and 12a. The flowdiffuser 802 can be held in place by the tapering configuration of thedistal end of the cannula, by adhesives, by ultrasonic welding, or byany other suitable means. Unlike the diffuser of FIG. 12, the distal endof the diffuser 802 is attached to the apex of the filter 806 by virtueof a linear shaft 808 said shaft running through the center of theexpanded filter. The shaft may be any shape which will not traumatizeblood components, and preferably comprises a rounded surface whichtapers outward in the distal direction. In this embodiment the flowdiffuser also diffuses cannula blood flow proximal to the filter. Thecannula 350 optionally contains openings 803 in its distal end 804 tofurther diffuse the cannula blood. In an alternate embodiment, blooddiffuser 802 is contained within cannula 350 but is not connected tofilter 806 said filter being supported as disclosed in FIG. 9.

It is to be understood that flow diffusers such as those of FIG. 11-14can be used in any blood filter device having a blood supply cannula andassociated filter, including the devices depicted in FIG. 2 and FIG. 3.Furthermore, the diffuser of FIG. 14 may be employed inside a cannulahaving a distal filter, such as in FIG. 7, thus creating a blood filterdevice with two filters, one proximal to and one distal to the cannulaopening.

In an alternative embodiment, shown in FIG. 15, a blood filter deviceand associated filter 906 include a generally cylindrical filter sleeve908 disposed circumferentially about the distal end of cannula 10, andattached to four control lines 902a, 902b, 904a, and 904b. Proximalforce on unroll control lines 904a and 904b unrolls filter sleeve 908from its depicted position so as to capture the filter as shown in FIG.16. In this embodiment, the manner of unrolling the filter sleeve isanalogous to the unrolling of a latex condom. Although the sleeve may beany shape, provided it both encases the device and rolls up in responseto the control lines, in a preferred embodiment the sleeve has acircular cross-section.

In FIG. 15 the filter sleeve 908 is rolled back distal to the filter toallow the filter to be fully expanded. FIG. 15 shows a cross-sectionalcut-away of the sleeve. The full sleeve, not depicted, is a continuouspiece surrounding the cannula about a 360 degree axis. In a preferredembodiment, a circular condom-like sleeve is attached at theouter-diameter of the cannula along the arc of circle 910. Thecondom-like sleeve has a distal opening to permit exit of the cannulatip. In a preferred embodiment a pair of control lines 902a and 904aenter a control lumen at points 928 and 929 respectively and run insidecontrol lumen 922 adjacent the cannula lumen until exiting the controllumen at a proximal point on the cannula (not shown). In the preferredembodiment, control lines 902b and 904b similarly enter and exit asecond control lumen 924 at points 926 and 927 respectively, said pointslocated 180 degrees from the first lumen on the cannula's outerdiameter.

As shown in FIG. 16, unroll control lines 904a and 904b are attached tosleeve 908 at points 914 and 916 respectively, said points located atthe proximal end of the sleeve. Consequently, when sleeve 908 isrolled-up, as shown in FIG. 15, points 914 and 916 are rolled into thecenter of the nautilus-shaped lip of sleeve 908 while unroll controllines 904a and 904b are rolled-up along side the sleeve.

In contrast, roll-up control lines 902a and 902b are attached to thecannula at points 918 and 920 respectively. Points 918 and 920 arelocated on arc 910. When the sleeve is rolled-up as shown in FIG. 15 theroll-up control lines 902a and 902b run from their respective points ofattachment 918 and 920, along the exposed side of the rolled-up sleeve,and enter the control lumens 922 and 924 at points 926 and 928respectively. After entering the control lumens, the roll-up linesproceed through the control lumens until exiting at points (not shown)proximally located on the cannula.

FIG. 16 shows the same blood filter device with blood cannula andassociated filter as FIG. 15 but with the sleeve 908 fully unrolled andcapturing filter 906. The unrolled sleeve provides a compact, smoothprofile for the device's introduction to and retraction from a vessel.In order to unroll the sleeve from the FIG. 15 position the unroll lines904a and 904b of FIG. 16 are pulled in a proximal direction, away fromthe cannula tip. Consequently, points 914 and 916 are positioned at theproximal end of unrolled sleeve 908.

When the sleeve is in the unrolled state, the roll-up control lines 902aand 902b run from points 918 and 920 respectively, along the undersideof the sleeve 908, around the proximal end of the sleeve, and thendistally along the outer side of the sleeve before entering the controllumens 922 and 924 at points 926 and 928 respectively. After entering atpoints 926 and 928, the roll-up control lines 902a and 902b travelthrough the control lumens until exiting the control lumens at points(not shown) located at the proximal region of the cannula. When thesleeve is in the unrolled position as shown in FIG. 16, the roll-uplines may be pulled in a proximal direction, away from the cannula tip.Pulling the roll-up lines causes the sleeve 908 to roll-up untilreaching the rolled-up state shown in FIG. 15. In a preferred method ofuse, the sleeve 908 is unrolled prior to insertion of the cannula in avessel, rolled up during mesh deployment, and once again unrolled priorto cannula retraction.

FIG. 17 shows a cross-sectional detail of the sleeve 908 in the unrolledstate, with emphasis on the points of attachment for the control lines.In the FIG. 17 embodiment, the sleeve, which is a continuous about 360degrees (not shown), is directly connected to the two roll-up lines 902aand 902b at points 918 and 920 respectively. Alternatively, the roll-uplines are attached directly to the cannula at points neighboring 918 and920 located immediately under the distal end of the sleeve. Pulling theroll-up lines in a proximal direction, as shown by the arrows in FIG.17, causes the sleeve to roll-up like a condom. Accordingly, the sleevematerial should be thin enough to avoid bunching and to provide smoothrolling in reaction to proximal force exerted by the roll-up lines. In apreferred embodiment, the sleeve is made of latex, with a thickness ofbetween 3 and 14 thousandths of an inch. In a more preferred embodiment,the sleeve is made of latex with a thickness of between 4 and 16thousandths of an inch. The invention may also use silicone or anothersilastic, biocompatible material to construct the sleeve. Othermaterials as are known in the art may permit use of a sleeve with athickness of less than 6 thousandths of an inch provided the materialgives suitable assurances against breaking or tearing.

FIG. 18 is a three-dimensional depiction of the cannula 350, filter 906and sleeve 908, with sleeve 908 in the rolled-up state. In oneembodiment, the filter 906 is located distal to the cannula opening suchthat cannula output is filtered upon exiting the cannula. In anotherembodiment the filter is located proximal to the cannula opening suchthat cannula output is downstream of the filter. The cannula opening mayoptionally have a planar diffuser 932. Filter 906 is made of a meshwhich is contiguous with a sealing skirt 930. With the exception ofentrance point 933 both the roll-up and unroll lines enter and exit thecannula at points not shown. In a preferred embodiment, the controllines attach to a control line actuating mechanism such as a capstan,ring or pulley (also not shown). In this embodiment, the structureadapted to open and close the filter may be an umbrella frame (notshown), such as depicted in FIG. 1, or alternatively an inflationballoon (not shown), such as shown in FIG. 7 and FIG. 9. The FIG. 18embodiment may be used with any of the various means to actuate thestructure as described herein.

Pulling unroll control lines 904a and 904b in a proximal directioncauses the capture sleeve to roll out over the top of the filter.Subsequently pulling the roll-up control lines 902a and 902b in aproximal direction rolls-up the capture sleeve thereby permitting filterdeployment. In FIG. 18, the unroll lines are oriented at an angle of 180degrees from one another along the circumference of the filter (thus904b not shown). The roll-up lines 902a and 902b are similarly orientedat an angle of 180 degrees from one another. However, as with theinventions of FIG. 15-17, this embodiment may employ any number ofcontrol lines spaced at varying differences around the outer diameter ofthe filter sleeve.

FIG. 19 shows an alternative embodiment wherein one control ring 936controls rolling and unrolling of the sleeve 934 with the assistance ofa pulley mechanism. The control ring 936 is movable in both the proximaland distal directions along the outer diameter of the cannula (notshown). Control ring 936 is directly attached to unroll control lines904a and 904b and attached to roll-up control lines 902a and 902bthrough pulley 934. Proximal movement of the control ring causes thesleeve 908 to unroll. Distal movement conversely causes sleeve 908 toroll up.

In another embodiment of the blood filtration device, as shown in FIG.20, the cannula 350 contains a collapsible or deformable section 938such that the cannula can accommodate the filter 906 and filter seal907, as well as other filter components. The collapsible section 938 ismade out of an elastomeric material such as latex or silicone. Inanother embodiment the collapsible section is a double walled balloon.In a preferred embodiment the section is made of a flexible materialwith built in memory such that the collapsible walls automaticallyreturn to their non-collapsed state when deployment force expands thefilter means. The collapsing section begins proximal to the filter seal907 when the filter is in its collapsed state. In the embodiment shown,the collapsing section 938 begins just proximal to the site of thefilter seal 907 and has a length equal to the length of the filter andfilter seal. In an alternative embodiment, the collapsing sectionextends to the tip of the catheter from just proximal to the filterseal. The deformable section collapses radially inward when thefiltration assembly is closed in order to produce a low-profile distalend to the cannula. Thus, a portion of the radial volume of the cannulais occupied by the filtration assembly when the filtration assembly isdeployed; however, the blood flowing through the cannula subsequentlyblows the deformable cannula walls outwards to allow the flow of bloodthrough the entire cannula diameter.

In another embodiment of a blood filtration device, shown in FIGS. 21and 22, the cannula 350 is composed of a medically acceptable elasticmaterial, such as latex, silicone, rubber, and the like. As shown inFIG. 22, the cannula has an intrinsic length and diameter whichcharacterizes the cannula when it is not under axial stress. Theintrinsic length and diameter of the cannula vary according to vesselsize. The cannula may be closed ended with a cap diffuser of the typedisclosed in FIG. 11. Alternatively, the cannula may be partially closedat the tip as in FIG. 12.

As shown in FIG. 21, a stylet 944 is placed in the cannula 350 andengages the cannula tip. In an alternative embodiment, the styletengages a ring suspended at the opening of an open tip. When insertedfully into the cannula, the lengthy stylet 944 engages the distal tip ofthe cannula and axially stretches the cannula body as shown. In this waythe cannula is stretched so as to reduce cannula diameter. A finger grip946 secured to the proximal end of the stylet includes latch member 948.The latch member engages a recess 950, formed on a proximal fitting 952of the cannula, in order to maintain the cannula's stretchedconfiguration. After insertion in the vessel, the elastic cannula isradially expanded and shortened by depressing latch member 948 andwithdrawing the stylet as in FIG. 22.

In this embodiment, filter 908 is fixed to the outer diameter of theunexpanded elastic cannula 350 by tether lines 954 and 956 such thatwhen the stylet is introduced cannula extension causes the tether linesto go taut. This in turn causes the filter to contour to the cannula.Conversely, as shown in FIG. 22, when the stylet is removed the cannulashortens thereby permitting expansion of the filter. Although variousbiasing and filter opening mechanisms may be used, in a preferredembodiment, the filter itself is made of memory-wire biased to an openstate.

In another embodiment shown in FIGS. 23 and 24, the distal cannulaportion 960 upon which the filter assembly 962 is mounted is, at leastin part, a radially flexible material or composite construction which isnormally in a necked down, contracted position. This allows thecontracted filter assembly 962 to create as small of a profile aspossible for insertion into the blood vessel. The necked-down portion964 of the distal cannula is opened by inserting a close fittingexpander 966 through the necked-down portion. The expander 966 has adistal end 967. As a result of the expander insertion, the filterassembly 962 exhibits an extruding profile relative to the outercontours of the distal cannula. Optionally as shown in FIG. 24, thefilter assembly 962 may be fully deployed by a deployment mechanism (notshown), as previously described herein. In both FIGS. 23 and 24, theexpander is fixed relative to the proximal cannula 968. Both are moveddistally relative to the distal cannula so as to insert the expanderinto the collapsible section. Alternatively, the expander 966 may moveindependent of the proximal cannula 968.

In another embodiment shown is FIGS. 25 and 25A to 25D, cannula 350includes filter 906 having skirt 970 disposed around its outermost edge.Skirt 970 is an elasticmeric strip of material (e.g., silicon or othersuitable material) attached to the proximal edge of the filter mesh.Skirt 970 forms a compliant edge which conforms to vessel lumentopography and gives a better seal with the vessel lumen when the filteris deployed. Moreover, the compliant edge 970 allow for changes in thevessel interior dimension as the vessel pulses from systole to diastole.Both unroll control lines 904a and 904b, as well as roll-up controllines 902a and 902b (not shown) are routed through tube 978 and thenthrough the cannula housing at location 971 and thereafter ride withintubing 972 to the point where they are manipulated outside of the body.In addition to the roll-up and unroll control lines, a fifth controlline is also carried through tube 972 and location 971 for the purposeof operating the umbrella frame 973 depicted in FIG. 25. This controlline can ride either inside or outside of tube 978. The umbrella frameconsists of a series of primary struts 974 extending from the distal toproximal end of the mesh and disposed circumferentially thereabout, anda series of secondary struts 975. Struts 975 connect at their proximalend to struts 974 and at their distal end are slideably connected to theaxis of the conical filtration mesh. Secondary struts 975 thereforeoperate to open and close the expansion frame between a radiallyexpanded and radially contracted condition.

In another embodiment shown in FIG. 26, cannula 350 includes on itsdistal end a "windsock" or open-ended sleeve 976 which is either aporous mesh, a non-porous material (e.g., silicon), or a non-porousmaterial with holes which allow some degree of lateral blood flow. InFIG. 26, the windsock cannula is shown deployed within aorta 99. As canbe seen, embolic debris dislodged upstream of the cannula will becarried through the windsock 976 and will exit the distal opening 977.Sleeve 976 thereby prevents passage of embolic material laterally in theregion of the carotid arteries and thereby prevents or reduces theoccurrence of embolic material reaching the brain. At the same time,however, the windsock apparatus overcomes difficulties associated withfilter blockage due to blood clotting and buildup of debris bydelivering a high volume of blood downstream of the carotid arterieswithout the need to pass laterally through the sleeve.

In another embodiment, a filter is provided in the form of a "lobstertrap" as depicted in Reger et al., U.S. Pat. Nos. 5,108,419 (FIGS. 2,14, 15) and 5,160,342, incorporated herein by reference. A filter ofthis construction allows debris into an entrapment chamber through asmall opening. A series of other small openings generally are includedwithin this structure, and debris therefore advances one-way, distallythrough the structure. However, once the material enters the structureit cannot get out, and thus, if there is a momentary reversal of bloodflow within the vessel, embolic debris cannot wash away from the filter.

It is to be understood that the blood filtration devices of FIG. 15-FIG.26, as well as the lobster trap, may optionally employ any elongatedinsertion member in place of blood cannula 350. The elongated insertionmember need not contain a lumen.

As a purely illustrative example of one of the methods of filteringblood as disclosed herein, the method will be described in the contextof cardiac bypass surgery as described in Manual of Cardiac Surgery d.Ed., by Bradley J. Harlan, Albert Spar, Frederick Harwin, which isincorporated herein by reference in its entirety.

A preferred method of the present invention may be used to protect apatient from embolization during cardiac surgery, particularly cardiacbypass surgery. This method includes the following steps: introducing amesh into an aorta of the patient; positioning the mesh to coversubstantially all of the cross-sectional area of the aorta preferablyproximal to the carotid arteries so that the mesh may entrap embolicmatter or foreign matter in the blood before it can escape to the brain;adjusting the mesh to maintain its position covering substantially allof the cross-sectional area of the aorta; and removing the mesh and theentrapped foreign matter from the aorta. A variant comprises placing acylindric mesh at the level of the take off of the cerebral vessel todivert emboli otherwise destined for the brain to other parts of thebody.

During the cardiac surgery, the aorta is clamped a number of times.Because clamping the aorta dislodges atheromatous material from thewalls of the aorta, which is released into the bloodstream, the meshmust be positioned within the aorta before clamping begins. Atheromatousmaterial also accumulates behind the clamps during the surgery and,because removal of the clamps releases this material into thebloodstream, the mesh must be maintained within the blood stream forabout four to ten minutes after removal of the clamps. Because the aortais often a source of much of the atheromatous material that iseventually released into the bloodstream, it is preferable to place themesh in the aorta between the heart and the carotid arteries. Thisplacement ensures that foreign matter will be entrapped before it canreach the brain.

For illustration purposes, the method for filtering blood will bedescribed in connection with the device depicted in FIG. 4. After apatient has been anaesthetized and the patient's chest has been openedin preparation for the bypass surgery, the cannula 205, ranging fromabout 22 to about 25 Fr. O.D. in size, is introduced into an incisionmade in the aorta. The cannula 205 is sutured to the aortic wall, andthe heart is paralyzed. The device 10 is stored in a closed positionwithin the cannula 205, in which the balloon 230 is deflated and foldedin upon itself, and the mesh 220 is closed. The cannula 205 and thedevice 10 will not interfere with other equipment used in the surgicalprocedure.

The blood filter device 10 is then inserted into the aorta through thecannula 205 via the tie lines 250. Saline is introduced into the balloon230 through the actuation assembly 260 from an extracorporeal reservoir,and the device 10 gradually assumes an open position in which theballoon 230 is inflated in a donut-shape and the mesh 220 is opened tocover substantially all of the cross-sectional area of the vessel. Inthe opened position, the device 10 is ready to entrap foreign matter inthe blood flow. By adjusting the amount of saline introduced into theballoon 230, the surgeon may control the amount of inflation andconsequently the degree to which the mesh 220 is opened. After thedevice 10 has been actuated, blood from a bypass machine is introducedinto the aorta through the cannula 205 and is filtered by the device 10.

To block the flow of blood back into the heart, the surgeon cross-clampsthe aorta, or, in an alternative procedure, balloon occludes the arteryor aorta. Cross-clamping and/or balloon occluding the aorta dislodgesatheromatous material from the walls of the aorta and releases it intothe blood flow. Because cross-clamping is done upstream from the device10, the atheromatous material will be filtered from the blood by thedevice 10. While the aorta is cross-clamped, the surgeon grafts one endof a vein removed from the patient's leg on to the coronary artery.After the surgeon checks the blood flow to make sure there is noleakage, the aortic clamps are removed. Atheromatous materialaccumulates behind the clamps and, when the clamps are removed, thismaterial is released into the blood flow, which will be filtered by thedevice 10. The flow rate from the bypass machine is kept low to minimizeembolization, and the heart is made to beat again.

During surgery, the position of the mesh may require adjustment tomaintain its coverage of substantially all of the cross-sectional areaof the aorta. To accomplish this, the surgeon occasionally palpates theoutside of the aorta gently in order to adjust the device 10 so that themesh 220 covers substantially all of the cross-sectional area of theaorta. The surgeon may also adjust the location of the device 10 withinthe aorta.

The device 10 may also be used in conjunction with TCD visualizationtechniques. Through this technique, the surgeon may actuate the device10 only when the surgeon expects a flurry of emboli such as duringaortic cannulation, inception, and termination of bypass, aorticclamping, and clamp release.

The surgeon then clamps the aorta longitudinally to partially close theaorta, again releasing the atheromatous material to be filtered by thedevice 10. Holes are punched into the closed off portion of the aorta,and the other end of the vein graft is sewn onto the aorta where theholes have been punched. The aortic clamps are then removed, againreleasing accumulated atheromatous material to be filtered from theblood by the device 10. The surgeon checks the blood flow to make surethere is no leakage. The heart resumes all the pumping, and the bypassmachine is turned off, marking the end of the procedure.

The saline is then removed from the balloon 230 via the actuationassembly 260, deflating the balloon 230 and closing the mesh 220 aroundthe entrapped emboli. The device 10 is then retracted into the cannula205 by pulling the tie lines 250 into the cannula 205. If the balloon230 has not been deflated sufficiently before retraction, excess salinemay be squeezed out of the balloon 230 as it is retracted into thecannula 205. Finally, the cannula 205 and the device 10, along with theentrapped emboli, are removed from the body. Because the device 10 is inplace throughout the procedure, any material released during theprocedure will be entrapped by the device 10.

When the device 10 is used in conjunction with other invasiveprocedures, the dimensions of the device should be adjusted to fit thevessel affected. An appropriate mesh also should be chosen for bloodflow in that vessel. In use, the device may be positioned so that it isplaced downstream of the portion of the vessel that is affected duringthe procedure, by clamping or other step in the procedure. For example,in order to entrap emboli material in a leg artery, the cone-shapedfilter can be placed such that the cone points toward the foot.

An advantage of the devices and methods of the present invention and themethods for filtering blood described herein is that it is possible toentrap foreign matter resulting from the incisions through which thedevices are inserted. Another advantage of the devices of the presentinvention is that the flexibility of the inflatable balloon allows it toconform to possible irregularities in the wall of a vessel.

In other methods of the invention, the filter is decoupled from thecannula and the filter is disposed on an elongate member separate fromthe cannula. As such, while the cannula is inserted into the aortagenerally upstream of the aortic arch, the filter disposed on anelongate member may or may not be entered through the same incision asthe cannula. Thus, the filter may enter by any of the following routes;(1) through the cannula and deployed downstream of the cannula, (2)through the cannula and deployed upstream of the cannula, (3) throughthe left subclavian artery and deployed at a point either upstream ordownstream of the cannula, and (4) through the femoral artery andthereafter into the aortic arch and deployed either upstream ordownstream of the cannula. In other methods of the invention, the filteris deployed during stages of the cardiac surgery procedure and removedbetween certain stages.

The cerebral embolic signals during coronary artery bypass grafting areas follows (expressed as percentage embolic release per event): cannulaon=2%, bypass on=6%, aortic cross clamp on=6%, aortic cross clampoff=21%, partial occlusion clamp on=7%, partial occlusion off=14%,bypass off=8%. Moreover, during the approximately 5.8 minute intervalbetween bypass on and aortic cross clamp on, approximately 4% of embolicmaterial is released. During the approximately interval betweenplacement of the cross clamp and removal of the aortic cross clamp, atime of approximately 38.8 minutes, about 13% of the embolic material isreleased. During the approximately 4.1 minute interval between removalof the aortic cross clamp and installation of the partial occlusionclamp, approximately 9% of embolic material is released. During theapproximately 9.7 minute interval between placement of the partialocclusion clamp and removal of the partial occlusion clamp,approximately 2% of embolic material is released. Finally, during the7.3 minute interval between removal of the partial occlusion clamp andturning bypass off, approximately 8% of embolic material is released.

Thus, in one embodiment, it is desirable to have a filter deploy shortlybefore cross clamp removal and removed shortly thereafter. In anotherembodiment, it is desirable to have a filter deploy only during theperiod just after cross clamp placement and removed after cross clampremoval. In still another embodiment, it is desirable to have the filterdeployed just before placement of the aortic cross clamp and maintaineduntil after removal of the aortic cross clamp. Alternatively, the filtermay be deployed before and removed after installation of the cross clampor removal of the cross clamp or placement of the partial occlusionclamp or removal of the partial occlusion clamp. In still anotherembodiment, the filter is deployed only during the interval betweenplacement and removal of the aortic cross clamp. Thus, in someembodiments it will be desirable to have the filter deployed onlytransiently for events of short duration, e.g., cannula on, bypass on,cross clamp on, cross clamp off, partial occlusion clamp on, partialocclusion clamp off, and bypass off. In other embodiments, it will bedesirable to have the filter deployed throughout a number of thesemanipulative events. In still other embodiments it will be desirable tohave the filter deployed only during one or more interval between thesemanipulative events. For a discussion of embolic staging during bypasssurgery the reader is referred to Barbut et al., Stroke 25:2398-2402(1994), expressly incorporated herein by reference.

While particular devices and methods have been described for filteringblood, once this description is known, it will be apparent to those ofordinary skill in the art that other embodiments and alternative stepsare also possible without departing from the spirit and scope of theinvention. Moreover, it will be apparent that certain features of eachembodiment can be used in combination with devices illustrated in otherembodiments. For example, the inflation system illustrated in FIG. 7 canbe used with any of the devices depicted in FIGS. 1-4. Accordingly, theabove description should be construed as illustrative, and not in alimiting sense, the scope of the invention being defined by thefollowing claims.

We claim:
 1. A method for protecting a patient from embolization,comprising the steps of:providing a blood filter device; introducing theblood filter device into the patient's aorta; deploying the filter at asite within the patient's aorta; blocking the aorta in a region upstreamof the site within the patient's aorta; and removing the blood filterdevice from the patient's aorta.
 2. The method of claim 1, furthercomprising the step of performing cardiac surgery on the patient.
 3. Themethod of claim 1, further comprising the step of performingcardiopulmonary bypass on the patient.
 4. The method of claim 1, whereinthe blood filter device has a filter adapted to operate at a site withinthe aorta of the patient, and to be removed thereafter.
 5. The method ofclaim 4, wherein the blood filter device comprises a cannula adapted toreceive a separately insertable filter.
 6. The method of claim 5,wherein the cannula includes a lumen, and wherein the filter is insertedinto the aorta through the lumen of the cannula.
 7. The method of claim6, wherein the lumen of the cannula receives blood from abypass-oxygenator machine.
 8. The method of claim 1, wherein embolicmaterial is generated and filtered before the blood filter device isremoved from the patient's aorta.
 9. The method of claim 1, wherein thefilter is deployed before the step of blocking the aorta.
 10. The methodof claim 1, wherein the filter is deployed after the step of blockingthe aorta.
 11. The method of claim 1, further comprising the step ofunblocking the aorta.
 12. The method of claim 1, further comprising thestep of unblocking the aorta before the blood filter device is removedfrom the aorta.
 13. The method of claim 1, wherein the step of blockingthe aorta includes clamping the aorta.
 14. The method of claim 1,further comprising the step of creating an incision in the aorta inorder to deploy the filter.
 15. The method of claim 1, wherein thefilter is deployed in the ascending aorta between the heart and carotidarteries.
 16. A method for protecting a patient from embolization,comprising the steps of:providing a blood filter device; introducing theblood filter device into the patient's aorta; blocking the aorta;deploying the filter at a site within the patient's aorta; unblockingthe aorta in a region upstream of the site within the patient's aorta;and removing the blood filter device from the patient's aorta.
 17. Themethod of claim 16, further comprising the step of performing cardiacsurgery on the patient.
 18. The method of claim 16, further comprisingthe step of performing cardiopulmonary bypass on the patient.
 19. Amethod for protecting a patient from embolization, comprising the stepsof:providing a cannula adapted to receive a separately insertablefilter; introducing the cannula into the patient's aorta; introducingthe filter through the cannula into the patient's aorta; deploying thefilter at a site within the patient's aorta; manipulating the aorta in aregion upstream of the site within the patient's aorta; and removing thefilter from the patient's aorta.
 20. A method for protecting a patientfrom embolization, comprising the steps of:providing a blood filterdevice; introducing the blood filter device into the patient's aorta;deploying the filter at a site within the patient's aorta while theheart is beating; and removing the blood filter device from thepatient's aorta.